Abstract
Objective of this study was to investigate the effect of different preservative systems used in the concentrated latex manufacturing industry on physical properties of the latex crepe made out of them. Unfractionated and unbleached (UFUB) crepe rubber manufactured from latices preserved with ammonia, tetramethylthiuram disulphide, zinc oxide and a 1:1 mixture of tetramethylthiuram disulphide (TMTD) and zinc oxide (LATZ) were subjected to examine their raw rubber properties. It was observed that UFUB crepe rubber manufactured out of either ammonia preserved, ZnO preserved or chemically untreated latices have better resistance to thermo-oxidative degradation compared to UFUB crepe rubber made out of both TMTD and LATZ preserved latex. Further, it was observed that neither ammonia nor ZnO has any effect on the thermal degradation of crepes made out of ammonia or ZnO preserved latex. It was clear from the results that the TMTD added as a component of the preservative system adversely affects the resistance to thermo-oxidative degradation as judged by PRI of crepe produced. Crepe rubber manufactured from TMTD preserved latex exhibits unusually lower PRI and a nitrogen content comparable with the normal UFUB crepe rubber. Skim crepe rubber which is considered a by-product of the latex centrifuging industry, usually records higher nitrogen percentages and lower PRI values. Therefore, evaluation of these two parameters could be used to differentiate skim crepe rubber from normal UFUB crepe rubber. It was also observed that TMTD has a strong negative impact on PRI of crepe rubber even at very low concentrations. It could be proposed that dimethylthiuram monosulphide (DMTMS) free radicals generated by thermal decomposition of TMTD are responsible for this PRI reduction.
Highlights
Natural Rubber Latex (NRL) exuded from Hevea tree is prone to deteriorate in quality due to activity of microorganisms on non-rubbers present in latex
Among the three chemicals, viz. ammonia, Zinc Oxide (ZnO), tetra methylthiuram disulphuide (TMTD), commonly used for preservation of NR latex, it was found that neither ammonia nor ZnO has any influence on the thermal degradation of rubbers
It was found that TMTD has a strong influence on thermal degradation of rubber as indicated by the low Plasticity Retention Index (PRI) values of crepe rubber produced
Summary
Natural Rubber Latex (NRL) exuded from Hevea tree is prone to deteriorate in quality due to activity of microorganisms on non-rubbers present in latex. Secondary preservative systems with low ammonia content in latex have been developed for the preservation of NR latex by John, et al It has become the widely used commercially accepted preservative system in the centrifuged latex industry. There are instances where inadequately preserved LATZ latex becomes unsuitable for the manufacture of centrifuged latex due to poor latex preservation procedures adopted in the field In such instances, it is necessary to convert this latex into an alternate form of natural rubber to recover the rubber. A study was carried out to investigate the raw rubber properties of crepe rubber manufactured from LATZ preserved field latex with the following objectives
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